1. Field of the Invention
The present invention relates to a circuit for current measurement and current monitoring and the use thereof for, for example, a functional unit of a motor vehicle.
2. Description of the Background Art
Conventionally, an operational amplifier is wired as a subtractor circuit, so that a first input potential of a negative input of the subtractor circuit is subtracted from a second input potential of a positive input of the subtractor circuit. Also, an offset voltage can be set by connecting the subtractor circuit to a certain potential. The effect of the offset voltage is that the output voltage of the subtractor circuit is the sum of the offset voltage and the differential voltage between the first and the second input potential. For current measurement, the first input and the second input are each connected to at least one contact of a measuring resistor.
DE 37 00 987 C2 discloses a device for the determination of electric voltage for processing by a microcomputer. The device is equipped with at least one analog/digital converter, which has a conversion width of n bits. The device is equipped with a digital/analog converter and a differential amplifier, which amplifies the difference between the voltage to be measured and the output signal of the digital/analog converter and supplies it to the at least one analog/digital converter of the microcomputer.
The microcomputer comprises means which control the conversion of, or one of the analog/digital converters into a first digital word and which provide the highest value bit of this word via the digital/analog converter to the differential amplifier. Moreover, the means control the conversion of the amplified difference between the voltage to be measured and the output signal of the digital/analog converter by means of, or one of the analog/digital converters into a second digital word. Moreover, from the first and second digital word, the means form a digital result, m+n bit wide, representing the voltage to be measured, so that the resolution of the measured voltage is m+n bits, where m<n. The amplification of the differential amplifier is k=2m. The digital/analog converter has a word width of m+1 bits. The microcomputer comprises means, which form a hysteresis during the transition from one lower measuring range, designated by the highest value bit of the converted voltage, to another.